Taylor Swift stunned fans at her concert in Los Angeles on Tuesday night (23Aug11) by welcoming Justin Bieber on to the stage for a special duet.The Love Story hitmaker was headlining at the Staples Center and she surprised the audience by bringing on the 17 year old during the show. The pair performed Bieber's hit track Baby and Swift was overwhelmed by the frenzied reaction from the crowd. In a series of posts on her Twitter.com page, she writes, "Dear amazing LA crowd tonight, God only knows what I'd be without you. "You think you've heard Loud screaming in your life... Then justinbieber comes out and does a surprise song during your show. Woah. Unreal." Bieber adds, "We should do that more often... great show! Much love."